This application is based upon the premise that the innate host response to oral commensal colonization 5 beneficial to the host. In other words, the protective response elicited by the host to oral commensal bacterial colonization in fact contributes to normal periodontal tissue functions with respect to prevention of disease. It is known that clinically healthy periodontal tissue contains a highly orchestrated expression pattern of select innate host defense components that are believed to function in protecting this tissue and the host from pathogens. Studies in germ-free mice have revealed that commensal bacterial colonization of the intestine stimulates host responses that contribute to the ontogeny of the intestine with respect to immune and tissue function. Therefore, we wish to test the hypothesis that: "Commensal oral bacteria contribute to the ontogeny of the innate host response found in clinically healthy periodontal tissue". We will examine this hypothesis in three Specific Aims. Specific Aim 1 will compare the periodontal innate post defense status in germ-free and conventionally reared mice to identify those host components regulated by commensal oral bacteria. This Aim will determine the contribution of commensal bacteria to the ontogeny of the innate host response in the periodontium. Specific Aim 2 will determine if P. gingivalls, a well-known periopathogen can alter the "beneficial homeostasis" established between the host and its commensal flora. n Specific Aim 3 changes in gingival epithelial cell TLR2 and TLR4 expression levels that may alter commensal homeostasis with the host will be determined. Since both microbial composition and innate host response expression patterns are dynamic and likely to change over time these last two Aims are potentially relevant to alterations in oral bacterial I host interactions that may occur with increasing age.